1. Field of the Invention
This invention relates to novel processes for improving rates and yields in hydrosilation reactions, those being addition reactions of compounds containing hydrosilyl groups, i.e., .tbd.SiH groups, to unsaturated compounds to form carbon-functional silicon compounds. In particular, the present invention relates to the use of a hydrosilyl compound as a promoter in these hydrosilation reactions.
2. Prior Art
The hydrosilation reaction was discovered in 1947 and is now one of the best known and most widely practiced reactions in organosilicon chemistry, including use in a wide variety of large scale commercial applications. This reaction has been the subject of several extensive reviews. l C. Earborn & R. W. Bott, Organometallic Compounds of the Group IV Elements (1968); E. Lukevics & M. G. Voronkov, Organic Insertion Reactions of Group IV Elements (1966).
A number of patents in the art have shown that platinum compounds can have important catalytic effects in these reactions.
U.S. Pat. No. 2,632,013 to Wagner et al, for example, is an early patent showing that various forms or compounds of platinum can be effective catalysts for hydrosilation reactions. U.S. Pat. No. 2,823,218 to Speier showed that chloroplatinic acid, a soluble form of platinum, was a particularly effective catalyst. A variety of additives to or derivatives of chloroplatinic acid have been claimed as offering some advantage over chloroplatinic acid, H.sub.2 PtCl.sub.6. None of these patents teaches the use of a second hydrosilyl compound used in combination with the soluble platinum catalyst to promote the rate or yields of the first reaction.
Of the many hydrosilation reactions taught in the prior art, very few involve the hydrosilation reactions between two different hydrosilyl compounds and one unsaturated compound. Moreover, that art which does discuss this area focuses on the competitive reactivity order of the hydrosilyl compounds with regard to the unsaturated compound. That is, the art teaches which of the two hydrosilyl compounds reacts better with a third unsaturated one; there is no teaching of the positive effect one such hydrosilyl compound might have on the other in increasing the yield of the hydrosilation reaction product, i.e., the product of the reaction between the hydrosilyl reactant and the unsaturated compound, or in decreasing the reaction time in the formation of such product.
For example, work by Bailey, D. L. Bailey, remarks at the 137th National Meeting of the American Chemical Society (Apr. 5-14, 1960), and by Benkeser, R. A. Benkeser, remarks at the 165th National Meeting of the American Chemical Society (Apr. 8-13, 1973), has established the competitive reactivity order H.sub.3 SiCl&gt;H.sub.2 SiCl.sub.2 &gt;Cl.sub.3 SiH for reactions with alkenes, this being the reverse of the reactivity order these compounds display when they are not competing with one another. The reversal occurs because the compounds, which are more reactive competitively, effectively reduce the reactivity of the other compounds, i.e., they have a negative effect on hydrosilation reactivity. The work done by Bailey did not study and did not note any promotional effects.
Other studies, have also concentrated on the competitive effect among hydrosilyl reactants. Ponomarenko et al in Izv. Akad. Nauk SSSR, Otdel. Khim. Nauk 1610 (1960); Engl. trans. in Bull. Acad. Sci. USSR, Chem. Sci. Section 1496 (1960).
In none of this prior art is there found an example of a second hydrosilyl compound having a positive effect on the reactivity of another hydrosilyl compound. This prior art always shows the two compounds in competition with one another rather than the one promoting the other in a non-competitive hydrosilation reaction.
Two Russian papers by Ponomarenko et al. do note such a positive effect, whereby Cl.sub.3 SiH and EtSiHCl.sub.2 increase yields of products from reactions of Et.sub.2 MeSiH with allyl ethers (CH.sub.2 .dbd.CH--CH.sub.2 OCF.sub.2 CFClH or CH.sub.2 .dbd.CHCH.sub.2 OCF.sub.2 CF.sub.2 H) using Pt/C (platinum on carbon) catalyst. In these cases, however, high temperatures (164.degree.-198.degree. C.) and long reaction times (3 hrs) were used. These studies also involved the use of insoluble platinum catalysts. The same workers reacted Et.sub.2 MeSiH with CH.sub.2 .dbd.CHCH.sub.2 OCF.sub.2 CF.sub.2 H using H.sub.2 PtCl.sub.6 at lower temperature/time (25.degree. C./30 min), but did not use a second hydrosilyl compound in the H.sub.2 PtCl.sub.6 -catalyzed reaction. The authors of those papers specifically commented that no promotional effects were observed in using a second hydrosilyl compound together with chloroplatinc acid in a hydrosilation reaction conducted under mild reaction temperatures.
Thus, the use of a second hydrosilyl compound and soluble platinum catalysts to promote the large rate and/or yield enhancements disclosed in the present invention under relatively mild temperatures has not been disclosed in the prior art, and is in fact contradicted by the above prior art.
There has also been some prior art in which chloroplatinic acid, H.sub.2 PtCl.sub.6, has been treated with Cl.sub.3 SiH or MeSiHCl.sub.2 to give solutions which served as hydrosilation catalysts. Benkeser, 90 J. Am. Chem. Soc., 1871 (1968). In those studies, however, the same reactant, i.e. Cl.sub.3 SiH, was evaluated as both the starting reactant and the promoter. No advantage in either rate or yield was found. Similarly, in studies involving MeSiHCl.sub.2, the MeSiHCl.sub.2 was evaluated as both the starting reactant and promoter, and again no promotional advantages were observed. In U.S. Pat. No. 3,576,027 to Fish, a catalyst was prepared by treating H.sub.2 PtCl.sub.6.6H.sub.2 O with Me.sub.2 SiHCl in a separate step, which catalyst was then isolated and used to catalyze a reaction of MeSiHCl.sub.2 with 1-octene. The catalyst there was formed in a precombination step rather than being generated in situ. Additionally, large promotional effects were not observed. These tests show once more that it would be quite unexpected to find that a second hydrosilyl compound, used in a hydrosilation reaction at mild temperatures, could actually promote the rates and yields of that reaction.
Thus, there is a need in the art for a process which can be applied to hydrosilation reactions, i.e., those between hydrosilyl groups and unsaturated compounds, which process is characterized by relatively mild temperatures and relatively fast rates, by relatively inexpensive catalysts from which the active catalysts of the invention are generated in situ, and by greatly enhanced yields of carbon-functional silicon compounds formed from the hydrosilation reaction.